tailieunhanh - Database Fundamentals by Robert J. Robbins

Only the examiner is allowed to be with you during the exam. Children or pets are not allowed in the vehicle during the exam and cannot be left unattended in the facility while the driving exam is under way. If you need to bring children or pets with you, you must bring someone along to take care of them. During the driving exam, the driver and the examiner must wear safety belts, as required by law. You will automatically fail the exam if you violate any traffic law or commit any dangerous action while taking the exam. . | Database Fundamentals Robert J. Robbins Johns Hopkins University rrobbins@ File N_drive jhu class 1995 1994 1995 Robert Robbins Database Fundamentals 1 What is a Database General A database is any collection of related data. Restrictive A database is a persistent logically coherent collection of inherently meaningful data relevant to some aspects of the real world. The portion of the real world relevant to the database is sometimes referred to as the universe of discourse or as the database miniworld. Whatever it is called it must be well understood by the designers of the database. File N_drive jhu class 1995 1994 1995 Robert Robbins Database Fundamentals 2 What is a Database Management System A database management system DBMS is a collection of programs that enables users to create and maintain a database. According to the ANSI SPARC DBMS Report 1977 a DBMS should be envisioned as a multi-layered system External Level individual user views External View 1 External View n Conceptual Level Enterprise-wide view Conceptual Schema Internal Level storage view Internal Schema Storage Level physical storage Physical Database File N_drive jhu class 1995 1994 1995 Robert Robbins Database Fundamentals

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